Ballast extension-submersion truss stable platform

ABSTRACT

To overcome high construction and deployment/installation costs of spar platforms that are typically employed in deep waters for oil and gas production, Ballast Extension-Submersion Truss Stable Platform (BEST Stable Platform) capitalizes on a minimized wave-zone buoyancy design to control platform water-plane area. With a truss connected ballast that could be positioned at different depths, the Best Stable Platform can be constructed in shallow water near a fabrication yard, and the entire assembly could be towed to a drill site where the extended and submerged ballast would provide operational stability. For horizontal stability, mooring lines are floated by water neutral-density means to remove anchor line curvature. Accordingly, mooring lines could be pulled straight under water to provide optimal horizontal resistance, thereby reducing the need for excessive mooring line pretension that increases platform loads. Savings are realized by not having to design floating platforms that must have extra capacity to accommodate added pretension.

CROSS REFERENCE TO RELATED APPLICATION

This Application is related to application Ser. No. 11/159,089.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

not applicable

INCORPORATED BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

not applicable

BACKGROUND OF THE INVENTION

As oil and gas operations extend farther and farther out into deeper ocean areas, new technology has facilitated the petroleum industry's ability to manage production in more difficult environments. However, there are challenges with current deep-water floating platform designs. Deep-draught platform transportation and deployment in deep waters requires installation of topside superstructure in mid ocean, which is challenging and expensive. At depth of 10,000 ft for example, mooring lines for horizontal stability are affected by catenary curvature flexibility of anchor cables or chains, and large horizontal platform movement results as mooring line curvature changes with varying ocean current forces on platform.

BRIEF SUMMARY OF THE INVENTION

Ballast Extension-Submersion Truss Stable Platform (hereinafter BEST Stable Platform) capitalizes on a minimized wave-zone buoyancy design to enable platform construction in shallow water and facilitates towing of entire structure to deployment location. At oil-production work site BEST Stable Platform ballast and its truss are lowered to ensure platform stability. For horizontal movement, mooring lines are floated by water density-neutral means to remove anchor line curvature. Therefore, mooring lines could be pulled straight under water to provide optimal horizontal resistance.

DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a deployed BEST Stable Platform.

FIG. 2 shows a BEST Stable Platform configuration in construction or transit.

FIG. 3 shows a straight water neutral-density mooring line.

DETAIL DESCRIPTION OF THE INVENTION

Current technology for oil and gas production requires flooding a spar in deep waters with subsequent lifting and installation of topside structures over the up-righted spar. The process is expensive as spars require substantial steel, and transporting components to drill site for assembly and lifting tremendous weight onto a floating spar add to the costs and technical challenges. The BEST Stable platform could be constructed with less steel, fabricated completely in shallow water at or near a dock or yard, and towed as a finished platform to a location for drilling and production.

FIG. 1 shows a BEST Stable Platform 10 which includes a reduced water-plane area section floating at waterline 20. The figure shows platform configuration as deployed over a drill site. Float 30 provides buoyancy to support the entire platform, and in comparison to spars, a horizontally extending float 30 can enclose a larger volume with less steel and can be fabricated at lower cost. Furthermore, float 30 offers greater dynamic drag against vertical oscillation than what a spar could provide. Truss 40 connects float 30 to ballast 50, extending and submerging ballast 50 to a sufficient depth to provide overall platform stability.

FIG. 2 shows the BEST Stable Platform as fabricated at a construction site and during transportation to a production area, with the platform floating at waterline 120. Truss 140 and ballast 150 are shown retracted to facilitate construction and transit. Truss 140 fits in a central hollow area used for drill pipe access, and truss 140 and ballast 150 are lowered when the platform is deployed over a drill site. It should be obvious to engineers and designers knowledgeable of the art that pontoons, floats, outriggers, or barges could be attached to the float for added stability before truss 140 and ballast 150 are lowered to the configuration shown in FIG. 1. Furthermore, principles of buoyancy and stability are well understood by practitioners knowledgeable of the art, and the intent of this patent is not to pontificate on size or dimensions, but to established a BEST Stable Platform configuration and a methodology for deployment and installation that reduces costs for offshore oil and gas production.

Catenary curvature of suspension cables and mooring lines is a mathematical solution that balances all forces applicable to any isolated segment of a cable or chain. Acting on each segment are three forces-top tension, bottom tension, and gravity on the segment, and the forces balance in static equilibrium. It is the incremental weigh from each additional segment that gives a mooring line 210 of FIG. 3 its catenary shape. In the case of a suspension bridge, the main cables are fixed, and everything is stable, but for a mooring line on the other hand, the platform is free to move. With catenary curvature changing due to variable forces from varying ocean current, large horizontal platform movement could not be inhibited. To increase horizontal stability, water neutral-density means 230 are attached to mooring line 220 to achieve free floatation in water; with the removal of gravity as a component in the catenary equation, mooring lines could be pulled straight to eliminate any catenary shape and thus the inherent curvature flexibility. It should be noted that the so called compliant tower used in off-shore production is compliant because the effectiveness of standard anchor cables to inhibit horizontal tower movement is limited.

The key to this invention is neutral density to water. If an anchor system has same density as water, gravity is removed from consideration. If a mooring line is made of steel, water neutral-density means would comprise a plurality of lighter-than-water floats. If on the other hand a mooring line is made of a material less dense than water, water neutral-density means would comprise a plurality of heavier-than-water weights. Engineers and designers can by chance select for mooring lines a material that has about the same density as water, but the resulting catenary removal is fortuitous, an outcome not previously anticipated. The petroleum industry has not figured out neutral density and instead tried to increase mooring line effectiveness by pretension and by adding weights onto anchor chains in attempt to offset catenary curvature changes, which is exactly opposite to the neutral density approach of this invention. 

1. A floating platform comprising: a platform body which includes a float; a truss; and a ballast; with said truss attached to said ballast; with said platform body having space to permit the truss to move up and down with respect to the platform body; and with the platform body capable of rigidly attaching the truss so as to position the ballast adjacent to said float or at extension-submersion depth.
 2. A mooring system comprising a mooring line and a plurality of water neutral-density means, with said mooring line and said plurality of water neutral-density means together effectively yielding about the same density of water.
 3. A mooring system comprising a mooring line made from a material with density about that of water. 